CBQE-1425 Stop install script when it could not uninstall old version

Change-Id: I34f6193f074e10eb961e6d668a5ca45f808ba4a7
Reviewed-on: http://review.couchbase.org/27151
Tested-by: Thuan Nguyen <soccon@gmail.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>